36Ar

3 6 Ar, or Argon-36, is the isotope of the noble gas argon that has a mass number of 36. It is one of the three stable isotopes of argon, the others being Argon-38 and Argon-40. Argon-36 has 18 protons (the atomic number of argon) and 18 neutrons, making it an even-even nucleus with a ground-state nuclear spin of zero.

Natural occurrence and properties

In nature, argon consists mainly of Argon-40, with Argon-36 contributing a small fraction. The natural abundance of Argon-36 is about 0.3–0.4% of total argon. Argon-36 is stable and does not undergo radioactive decay under normal conditions. Its atomic mass is approximately 35.9675 atomic mass units. Like other argon isotopes, Argon-36 is inert and exists as a colorless, odorless gas under standard conditions.

Origin and distribution

Argon-36 is produced in trace amounts in the cosmos and is present on Earth as a component of atmospheric argon. It is also found in minerals and rocks where noble gases are trapped. The abundance of Argon-36 is much lower than that of Argon-40, which is predominately produced by the decay of radioactive potassium-40.

Applications

Argon-36 is used as a tracer and reference isotope in noble gas geochemistry and hydrology. In mass spectrometry and isotope hydrology, its relatively low abundance helps in calibration and in studying atmospheric transport and groundwater processes.

Safety

Argon, including Argon-36, is an inert, non-toxic gas. Like all noble gases, it can act as an asphyxiant in confined spaces by displacing oxygen.

See also

Isotopes of argon, Argon, Potassium-Argon dating, Noble gas geochemistry.